Vectorborne diseases, especially those endemic to or emerging within temperate latitudes, are especially vulnerable to climate change, because their transmission depends upon the thermodynamics of viral replication and dissemination within the poikilothermic arthropod vector and upon both arthropod vector and vertebrate host population dynamics related to hydrology and ecosystem dynamics. California provides a unique opportunity to study the impact of climate change on vectorborne diseases, because an extensive arbovirus surveillance program has tracked mosquito and virus activity for well over 50 years within biomes extending from hot, dry deserts in the SE to cool rainforests in the maritime NW and from maritime coastal regions to the Sierra Nevada. Our proposed new research addresses the overarching hypothesis that global warming and associated climate change will increase the risk of mosquitoborne arbovirus transmission at temperate latitudes. Using the endemic encephalitides in California as a model system, we propose address this hypothesis through five objectives: 1) identify and model arboviral transmission parameters sensitive to climate change, 2) use probabilistic long range forecasts to project temporal changes in these climate sensitive relationships, 3) determine spatial variation in model outcomes to identify populations at greatest risk, 4) document potential risk scenarios for use by California and national health planners and mosquito control agencies, and 5) modify the existing surveillance and response plan to respond to and perhaps mitigate escalating risk. Our proposed new research extends on-going projects that incorporate climate variation and forecasts into the California Mosquitoborne Encephalitis Virus Surveillance and Response Plan, the current decision support system utilized by the California Department of Public Health and local mosquito control agencies to mitigate West Nile and other arboviruses. Utilizing our extensive historical dataset, we anticipate modeling and evaluating retrospective trends and then probablistic forecasts to ascertain the impact of climate change on mosquito abundance, arboviral transmission and human risk in California. PUBLIC HEALTH RELEVANCE: Although climate change projections for California vary, there is a general consensus that temperatures during the current century will rise, precipitation amount and timing will change, and ecosystem dynamics will be altered. Concurrently the risk from vectorborne diseases is expected to increase, because warming temperatures will expand virus distributions in time and space, enhance vernal amplification rates and extend transmission seasons. Public health intervention currently focuses on mosquito control, and our research will help health planners anticipate short and long term risk and initiate mitigation strategies.